Coated surfaces are ubiquitous in today's society. Objects from integrated circuit boards, to optical lenses, to counter tops, to aircraft have coated surfaces. The surfaces may be coated with a protectant, such as an epoxy primer or a chemical barrier, or may be coated with an aesthetic layer such as paint or a decorative polymer. Often times the thickness of such coatings must be held to very strict specifications. For example, there may be a weight limit for components on a mobile platform, such as an aircraft, train, bus or ship that are required to be coated with a primer. Often such components arrive from suppliers uncoated and near maximum weight. Therefore, care must be taken to make sure that an adequate amount of primer is applied without exceeding the weight requirements. Additionally, the primer may be a corrosion inhibitor or a coating for restricting fluid leaks, such as a gas or a liquid, and therefore, must be applied at a uniform thickness. An outer paint coating may also be applied. Although the paint may only be a decorative coating, accurate control of the thickness is no less important. The weight must be kept to a minimum and must be applied uniformly for peak performance of the mobile platform.
Typically the thickness of non-metallic coatings on objects made of metallic materials can be measured by several conventional commercial tools. However, more and more objects, or components of objects, are manufactured from composite materials such as carbon fiber epoxy, carbon Kevlar® or fiberglass. The thickness of non-metallic coatings on these materials is difficult to measure since the substrate, i.e. the uncoated object or component, is only semi-conductive at best.
In at least one known method of measuring a non-metallic coating on a semi-conductive composite substrate, the substrate is weighed, then coated, then weighed again and checked for balance. If the coating is suspected of being too thick or uneven, the coating may need to be removed and recoated. In many cases, such as with a mobile platform, a coated component may have to be disassembled and recoated. This can cause significant increase in the labor costs of measuring the thickness of the coating and significant increase in the risk of damage to the substrate/component. Another known method of measuring a non-metallic coating on a semi-conductive composite substrate is to use an ultrasonic measurement system. However, typically ultrasonic measurement systems are not sufficiently reliable to accurately measure the thickness of thin film coatings such as paint. In addition, the nature of ultrasonic measurement requires the technician to interpret complex waveforms that require extensive training and certification.
Therefore, it would be desirable to accurately measure the thickness of thin film non-metallic coatings on a semi-conductive substrate, such as an aircraft control surface component, without having to weight the substrate. This can significantly reduce the labor costs and the risk of damage.